This is a sample using 4 columns id quantity unit price and a dynamically added column that caucates the total

for the grand total you have to add a text box at the bottom of the page and summarize all values in the column 3

DataGridViewTextBoxColumn TotalColumn;
private void Form1_Load(object sender, EventArgs e)
{
// TODO: This line of code loads data into the 'productsDataSet.Prod' table. You can move, or remove it, as needed.
this.prodTableAdapter.Fill(this.productsDataSet.Prod);
dataGridView1[0,0].Selected = true;
dataGridView1.Columns[1].Visible = false;
dataGridView1.Columns[2].Visible = false;
TotalColumn = new DataGridViewTextBoxColumn();
TotalColumn.HeaderCell.Value = "Total";
dataGridView1.Columns.Add(TotalColumn);
TotalColumn.Visible = false;
dataGridView1.KeyDown +=new KeyEventHandler(dataGridView1_KeyDown);
}

private void dataGridView1_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Tab)
{
dataGridView1.Columns[1].Visible = true;
dataGridView1.Columns[2].Visible = true;
dataGridView1.Columns[3].Visible = true;
for (int i = 0; i < dataGridView1.Rows.Count; i++)
{
dataGridView1[3, i].Value = Convert.ToDouble(dataGridView1[1, i].Value) * Convert.ToDouble(dataGridView1[2, i].Value);

}

}

}

Thanks for replying, i have done all wt i wanted to but now i m facing another problem. when i enter a wrong product code a messagebox appeares but after that the control shifts on the next cell i.e. Product Name. I want that If i enter wrong product code the focus should remain on the current cell. Any idea

My first guess would be the CurrentCell property of the datagrid. For this property you have to know at whitch row you just entered the product code. This is an exemple within the CellValueChanged event of a datagrid:

private void grdSearch_CellValueChanged(Object sender, DataGridViewCellEventArgs e)
{
grdSearch.CurrentCell = grdSearch.Rows[e.RowIndex].Cells["colProdId"];
}